Type 3 porous liquids

ABSTRACT

This invention relates to a dispersion comprising porous particles dispersed in a liquid phase, wherein the porous particles comprise a zeolite and the liquid phase is a size-excluded liquid. The invention also relates to a method of adsorbing a gas into a liquid, comprising at least the step of bringing the gas into contact with the dispersion. In addition, the invention relates to an assemblage of the dispersion, the zeolite comprising a cavity and a gas contained within the cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application under 35 U.S.C. §371 of International Application No. PCT/GB2018/053168, filed on Nov. 1,2018, which claims priority to International Application No.PCT/GB2018/051279, filed on May 11, 2018, the content of each of whichis incorporated herein by reference in its entirety.

This invention relates to dispersions comprising porous particlesdispersed in a liquid phase, wherein the porous particles comprise azeolite and the liquid phase is a size-excluded liquid, as well as tomethods of preparing such dispersions. The invention also relates to amethod of adsorbing a gas into a liquid, comprising at least the step ofbringing the gas into contact with the dispersions. In addition, theinvention relates to an assemblage of such a dispersion, the zeolitecomprising a cavity and a gas contained within the cavity.

BACKGROUND

Liquid phases for the dissolution of gases are known. Solutions ofvarious amines in water, or other solvents, are known to dissolve CO₂and are applied industrially in natural gas “sweetening”. However, thesemethodologies comprise the use of toxic materials; are corrosive towardssteel, which limits their uses industrially; and require large amountsof energy to regenerate. They are also non-specific and therefore cannotbe used for specific or targeted gas separation. An glycol ether solventtype called Genosorb is utilised in industry for separating CO₂ fromCH₄. However, the CO₂ uptake of Genosorb is limited, as is itsselectivity for CO₂ over CH₄.

Porous solids such as zeolites are useful in molecular separation due totheir permanent porosity. Porous solid adsorbents have significantadvantages, for instance in terms of lower energy penalties inadsorption-desorption cycles when compared with their liquidcounterparts, but they are difficult to incorporate into conventionalflow processes. The use of solid zeolite Rho as an adsorbent for CO₂/CH₄separation is described in Palomino et al, Chem. Commun., 2012, 48,215-217.

Porous liquids (liquids with permanent porosity, or dispersions) for usein molecular separation have subsequently been developed. These porousliquids have been categorised into three different types (Chem. Eur. J.,2007, 13, 3020) as follows:

-   -   Type 1—neat liquid hosts comprising molecules having an internal        cavity, and that the molecules cannot collapse or        interpenetrate,    -   Type 2—host molecules having an internal cavity, the molecules        being dissolved in a solvents that cannot occupy the host's        cavities, and    -   Type 3—particles of a host molecular framework dispersed in a        liquid that cannot occupy the host's cavities.        Thus, each type of porous liquid comprises a “host” having a        cavity into which, for example, gas molecules could be absorbed.

Disadvantages of known porous liquids include that their preparationinvolves several steps and requires highly specialised expertise. Thesolvents used to prepare them are often volatile, which restricts theiruse in applications utilising reduced pressure to remove dissolvedgases. In addition, the solubility of gases in these liquids isdifficult to predict due to a lack of available data.

Liquids having improved properties, particularly high CO₂ uptake andimproved selectivity for CO₂ over CH₄, are sought. This can provideimproved efficiency in industrial processes where these properties areuseful, for example by reducing circulation rates.

STATEMENT OF INVENTION

This invention relates to a dispersion comprising porous particlesdispersed in a liquid phase, wherein the porous particles comprise azeolite and the liquid phase is a size-excluded liquid.

Generally, a dispersion is a system in which particles are dispersed ina continuous phase of a different composition. The term “dispersion” isused in relation to the invention to refer to a system in whichparticles of a porous solid are dispersed in a liquid phase or medium.The dispersion may optionally comprise additives, such as surfactants,in order to increase the stability of the dispersion. Such additives areknown to those skilled in the art.

It is known that some dispersions are time dependent before the start ofseparation of the solid particles in the liquid phase or medium,possibly based on requiring some form of agitation to continue as adispersion. The present invention is not limited to the stability ortransience of the dispersion.

More particularly, the dispersion may be a type 3 porous liquid.

In particular, the porous particles may be microparticles and/ornanoparticles. More particularly, the porous particles may bemicroparticles. Microparticles are generally defined as particles havinga mean diameter in the range 0.1-100 μm (ie 100-100,000 nm). Moreparticularly, the porous particles may have a mean diameter in the range0.1-2 μm (ie 100-2000 nm). Nanoparticles are generally defined asparticles having a mean diameter in the range 1-100 nm.

More particularly, the pores of the porous particles may comprisemicropores (ie that they have a pore diameter of less than 2 nm),mesopores (ie that they have a pore diameter in the range 2-50 nm) or amixture of micropores and mesopores.

In some embodiments, the zeolite may be selected from zeolite Rho,zeolite Na-Rho, ECR-18, ZSM-25 and PST-20. More particularly, thezeolite may be zeolite Rho.

Zeolites may be generally defined as aluminosilicate materials which arecrystalline and porous. Zeolite Rho is a type of zeolite which may bedefined as having an Si/AI ratio in the range 1-8, more particularly2-6. In particular, zeolite Rho may have a mean pore diameter of 1.9-6.0Δngstroms, more particularly 2.9-4.0 Δngstroms, even more particularlyabout 3.6 Δngstroms. In particular, it may have a pore volume of0.22-0.44 cm³g⁻¹, more particularly 0.24-0.33 cm³g⁻¹, even moreparticularly about 0.26 cm³g⁻¹. More particularly, zeolite Rho may havea body-centred cubic crystal structure.

A size-excluded liquid may be defined in the context of the invention asa liquid which is excluded from the pores (ie the cavities) within theporous particles. This can be because the size-excluded liquid has amolecular size which is too large to enter the pores of the porousparticles. Alternatively, entry into the pores of the porous particlesmay be thermodynamically or kinetically unfavourable.

In particular, the size-excluded liquid may be selected from a glycol;15-crown-5; a tertiary amine having substituted or unsubstituted aryl oralkyl substituents, for example each substituent can individually beC₆-C₁₀ substituted or unsubstituted aryl or alkyl; the tertiary aminemay be a trialkylamine where each alkyl group is individually C₆-C₁₀alkyl, more particularly C₇-C₉ alkyl, for example trioctylamine;2-(tert-butylamino)ethyl methacrylate; a trialkyl phosphate where eachalkyl group is individually C₂-C₆ alkyl, more particularly C₃-C₅ alkyl,for example tributyl phosphate; a dialkyl phthalate where each alkylgroup is individually C₆-C₁₀ alkyl, more particularly C₇-C₉ alkyl, forexample dioctyl phthalate; and bis(2-ethylhexyl) sebacate. Moreparticularly, the glycol may be a polyalkylene glycol. In particular,the polyalkylene glycol may be a polyethylene glycol or a polypropyleneglycol. More particularly, the polyethylene glycol may be selected froma polyethylene glycol dialkyl ether and a polyethylene glycolcarboxylate. In particular, the polyethylene glycol dialkyl ether may beselected from a polyethylene glycol dimethyl ether and a polyethyleneglycol dibutyl ether.

The polyethylene glycol dimethyl ether may be in the form of a mixturewith one or more other components. Example mixtures include:

(i) polyethylene glycol dimethyl ether with triethylene glycol dimethylether and bis(2-(2-methoxylethoxyl)ethyl)ether (for example, Genosorb1753—triethylene glycol dimethyl ether (4.9% w/w);bis(2-(2-methoxylethoxyl)ethyl)ether (<=13% w/w));

(ii) polyethylene glycol dimethyl ether with triethylene glycol dimethylether (for example, Genosorb 1900—triethylene glycol dimethyl ether(4.9% w/w)); and

(iii) polyethylene glycol dimethyl ether with diaryl-p-penylenediamines,triethylene glycol dimethyl ether andbis(2-(2-methoxylethoxyl)ethyl)ether (for example, Genosorb 300—mixtureof diaryl-p-penylenediamines (<1% w/w); triethylene glycol dimethylether (4.9% w/w); bis(2-(2-methoxylethoxyl)ethyl)ether (<=13% w/w)).

The polyethylene glycol dibutyl ether may be in the form of a mixturewith one or more other components. An example mixtures is polyethyleneglycol dibutyl ether with diaryl-p-penylenediamines (for example,Genosorb 1843—mixture of diaryl-p-penylenediamines>=0.25-<1% w/w)).

In particular, the zeolite may be zeolite Rho and the size-excludedliquid may be a polyethylene glycol dimethyl ether, a polyethyleneglycol dibutyl ether, 15-crown-5 or bis(2-ethylhexyl) sebacate. Moreparticularly, the zeolite may be zeolite Rho and the size-excludedliquid may be a polyethylene glycol dimethyl ether. Even moreparticularly, the zeolite may be zeolite Rho and the size-excludedliquid may be a polyethylene glycol dimethyl ether in the form of amixture with one or more other components as defined above.

In particular, the dispersion may comprise 0.1-50 wt % of the porousparticles, more particularly 5-40 wt %. Even more particularly, thedispersion may comprise 10-30 wt % of the porous particles, moreparticularly 10-15 wt %.

In the dispersion according to the present invention, the pores of theporous particles may be accessible to a gas. Optionally, the gas may beCO₂, CH₄, N₂, C₂H₄, C₂H₆, Xe, SF₆, C₃H₈ or H₂, or a mixture thereof.More particularly, the gas may be selected from CO₂ and CH₄, even moreparticularly the gas may be CO₂.

According to a further aspect of the present invention, there isprovided a method of adsorbing a gas into a liquid, comprising at leastthe step of bringing the gas into contact with a dispersion comprisingporous particles dispersed in a liquid phase, wherein the porousparticles comprise a zeolite and the liquid phase is a size-excludedliquid. More particularly, the dispersion may be as defined above.

In an embodiment, the gas is in a gas mixture and the gas is selectivelyadsorbed by the dispersion.

In particular, the gas may be CO₂, CH₄, N₂, C₂H₄, C₂H₆, Xe, SF₆, C₃H₈ orH₂, or a mixture thereof. More particularly, the gas may be selectedfrom CO₂ and CH₄, even more particularly the gas may be CO₂.

In particular, the method of adsorbing a gas into a liquid mayadditionally comprise, after the step of bringing the gas into contactwith the dispersion, the step of regenerating the dispersion. Moreparticularly, the regeneration step may comprise applying a vacuum tothe dispersion. In particular, the regeneration step may compriseheating the dispersion to a temperature of at least 30° C., moreparticularly at least 40° C., even more particularly at least 50° C. Inparticular, the steps of applying the vacuum and heating may be carriedout at the same time. More particularly, the steps of applying thevacuum and heating may be carried out for at least 10 minutes, even moreparticularly at least 20 minutes, more particularly at least 30 minutes.

According to a further aspect of the present invention, there isprovided a method of preparing a dispersion comprising at least the stepof: mixing (i) porous particles comprising a zeolite, and (ii) asize-excluded liquid. The porous particles may be as defined above. Thesize-excluded liquid may be as defined above. More particularly, thedispersion formed by the method may be as defined above.

Optionally, the mixing includes agitating, stirring, sonication orgrinding or a combination thereof. More particularly, the method maycomprise stirring the mixture.

According to a further aspect of the present invention, there isprovided an assemblage of a dispersion comprising porous particlesdispersed in a liquid phase, wherein the porous particles comprise azeolite and the liquid phase is a size-excluded liquid, wherein thezeolite comprising a cavity and a gas contained within the cavity. Moreparticularly, the gas may be CO₂, CH₄, N₂, C₂H₄, C₂H₆, Xe, SF₆, C₃H₈ orH₂, or a mixture thereof. In particular, the gas may be selected fromCO₂ and CH₄, even more particularly the gas may be CO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be further described by reference to the followingFigures which are not intended to limit the scope of the inventionclaimed, in which:

FIG. 1A shows Powder X-Ray Diffraction (PXRD) data comparing thetheoretical pattern for zeolite Rho and the pattern for the zeolite Rhomade in the examples both before and after calcination at 500° C. for 8hours,

FIG. 1B shows PXRD data comparing as made zeolite Rho, Genosorb 1753,and 12.5 wt % and 25 wt % dispersions of zeolite Rho in Genosorb 1753,

FIG. 2 shows a Scanning Electron Microscope (SEM) image of the as madezeolite Rho,

FIG. 3 shows the CO₂ uptake of Genosorb 1753 at three differenttemperatures and at pressures of from 1-5 bar,

FIG. 4 shows the CO₂ uptake of a 12.5 wt % dispersion of zeolite Rho inGenosorb 1753 at three different temperatures and at pressures of from1-5 bar,

FIG. 5 shows the CO₂ uptake of a 25 wt % dispersion of zeolite Rho inGenosorb 1753 at three different temperatures and at pressures of from1-5 bar,

FIG. 6 shows the CO₂ solubility of a 12.5 wt % dispersion of zeolite Rhoin Genosorb 1753 before use, after use and regeneration at 25° C., andafter use and regeneration at 50° C., and

FIG. 7 shows a Parr reactor used in the high pressure gas updatestudies.

EXAMPLES

Synthesis

There are two reported methods to synthesize zeolite Rho according toliterature. For the current study of zeolite Rho, method 1 was used tosynthesize high crystallinity material.

Method 1 (see Palomino et al, Chem. Commun., 2012, 48, 215-217):18-crown-6 ether (4.70 g, 17.78 mmol), cesium hydroxide (3.53 g, 23.54mmol) and sodium hydroxide (1.70 g, 42.50 mmol) were dissolved in 30 mlof deionised water. Sodium aluminate (6.60 g, 32.65 mmol) was added tothis solution and stirred until fully dissolved. Ludox AS-40 colloidalsilica (52.5 g, 873.8 mmol) was then added. The resulting mixture wasstirred overnight at room temperature under atmospheric pressure. Theobtained precursor mixture was then placed in a Teflon-lined stainlesssteel autoclave at 398K for 3 days for crystallization. The resultingzeolite Rho was then washed with deionised water by filtration untilneutral and calcined at 773K for approximately 3 hours to remove theorganic template (18-crown-6).

Method 2 (see Mousavi et al, Ceramics International, 39 (2013),7149-7158): Caesium hydroxide (1.91 g, 12.75 mmol) and sodium hydroxide(3.274 g, 81.75 mmol) were dissolved in 20 ml of deionised water. Sodiumaluminate (3.94 g, 19.51 mmol) was added to this solution and stirreduntil fully dissolved. Ludox AS-40 colloidal silica (33.88 g, 563.9mmol) was then added. The resulting mixture was stirred overnight atroom temperature under atmospheric pressure. The obtained precursormixture was then placed in a Teflon-lined stainless steel autoclave at358K in an oil bath for 7 days for crystallization. The resultingzeolite Rho was then washed with deionised water by filtration untilneutral.

Method 3: Caesium hydroxide (1.91 g, 12.75 mmol) and sodium hydroxide(3.274 g, 81.75 mmol) were dissolved in 20 ml of deionised water. Sodiumaluminate (3.94 g, 19.51 mmol) was added to this solution and stirreduntil fully dissolved. Ludox AS-40 colloidal silica (33.88 g, 563.9mmol) was then added. 400 mg of crystalline zeolite Rho (seeding) wasthen added to the resulting mixture and stirred overnight at roomtemperature under atmospheric pressure. The obtained precursor mixturewas then placed in a Teflon flask at 358K in oil bath for 7 days forcrystallization. The resulting zeolite Rho was then washed withdeionised water by filtration until neutral.

The zeolite Rho data below is a result of testing carried out onmaterial made by Method 1.

The dispersion (also sometimes referred to as a “porous liquid”) wasprepared by mixing Genosorb 1753 and zeolite Rho by stirring thecomponents in laboratory flask until formation of homogeneousdispersion, typically about 15 mins. Other missing techniques such asgrinding, milling or sonicating can also be used.

Characterisation

The zeolite Rho-Genosorb 1753 porous liquid was characterized by PowderX-Ray Diffractometer (PXRD), Thermo-gravimetric Analysis (TGA) andInfrared Spectroscopy (IR). The PXRD spectrum of zeolite Rho in Genosorbporous liquid (see FIG. 1B) shows an identical pattern to that of theoriginal zeolite Rho (see both FIGS. 1A and 1B). This confirms that thezeolite components remain intact and crystalline after mixing withGenosorb.

An SEM image of the original zeolite Rho (ie not as a dispersion) isshown in FIG. 2 . This demonstrates that the particle size is around1.0-1.2 μm.

Gas Uptake Studies

Low pressure measurement (c.a. 0.8 bar condition; 25° C.)—Gas solubilitystudies were carried out by using a volumetric technique based on anisochoric method (see S. L. James et. al.; Nature, 527, 216).

All the measurements were carried out at around 0.8 bar and 298K. Theresults show that the addition of zeolite Rho to commercial solventGenosorb 1753 increases the CO₂/CH₄ selectivity significantly (see Table1 below). The zeolite Rho does not lose its gas capacity and the gasuptake is predictable.

TABLE 1 12.5 wt % 25 wt % Genosorb Zeolite Rho in Zeolite Rho in 1753Genosorb Genosorb CO₂ solubility* 0.209 mmol/g 0.475 mmol/g 0.738 mmol/g(9.234 mg/g) (20.923 mg/g) (32.499 mg/g) CH₄ solubility

0.055 mmol/g 0.043 mmol/g 0.027 mmol/g (0.882 mg/g) (0.6463 mg/g)(0.4383 mg/g) CO₂/CH₄ c.a. 3.8 c.a. 10.32 c.a. 23.06 *from large volumegas rig (V2)

from small volume gas rig (V1), error is large due to small amount ofCH₄ uptake

High Pressure measurement (1-5 bar, 25° C.-75° C.)—High pressure gassolubility studies were carried out by using Parr reactor based on amass flow (see A. M. Orozco et. al., Industrial Crops and products,2013, 44, 1 for a similar experimental set-up).

All the measurements were carried out from 1 to 5 bar at 298K, 323K and348K. The high pressure measurements also show predictable outcomes.Table 2 below, and FIGS. 3-5 , show the CO₂ uptake of Genosorb 1753, a12.5 wt % dispersion of zeolite Rho in Genosorb 1753 and a 25 wt %dispersion of zeolite Rho in Genosorb 1753. Table 3 below shows theexperimental values for pure zeolite Rho at 298K, plus the predictedvalues for the 12.5 wt % zeolite Rho in Genosorb 1753 and 25 wt %zeolite Rho in Genosorb 1753 dispersions.

The measured CO₂ solubility of the dispersions is comparable to itspredicted value at low pressure but slightly less than the predictedvalue at high pressure. The high pressure gas uptake measurements showthat the addition of zeolite Rho to Genosorb 1753 solvent significantlyenhances CO₂ uptake and the operational range for a temperature pressureswing adsorption/desorption system.

TABLE 2 12.5 wt % Zeolite 25 wt % Zeolite Genosorb Rho in Genosorb Rhoin Genosorb 298K 323K 348K 298K 323K 348K 298K 323K 348K 1 5.478 5.0443.669 16.457 11.476 7.919 30.024 21.639 15.234 bar 2 11.331 9.687 7.42329.015 19.852 14.160 48.327 33.558 24.342 bar 3 17.493 14.571 11.72735.968 36.580 19.339 58.322 41.623 30.804 bar 4 24.221 19.598 16.20642.717 32.829 24.000 65.377 50.361 36.102 bar 5 31.471 25.089 20.85349.862 37.909 29.408 72.444 58.028 41.274 bar

TABLE 3 298K Experimental Theoretical 12.5 Theoretical 25 pure ZeoliteRho wt % Zeolite Rho wt % Zeolite Rho 1 bar 108.12 18.31 31.14 2 bar170.00 31.16 51.00 3 bar 200.57 40.38 63.26 4 bar 216.69 48.28 72.34 5bar 228.68 56.12 80.77

Reversibility/Regeneration

Ease of material regeneration is a useful property which can provide areduction in regeneration cost. It is difficult to achieve byamine-based technology nowadays due to the high energy penalty. Thedispersions of the invention are understood to be easily regenerated byapplying mild heating or vacuum. As shown in FIG. 6 , the porous liquid(12.5 wt % zeolite RHO in Genosorb 1753) shows about a 62.5% recovery inCO₂ uptake capacity when it has undergone a room temperatureregeneration under vacuum for 30 minutes. However, CO₂ uptake capacityrecovers to around 92% when the same regeneration conditions are used,but the temperature is increased to 50° C.

Additional CO₂ Uptake Studies

Further dispersions comprising combinations of porous particles withvarious liquids were prepared by mixing the porous particles with theliquid as described above. The dispersions produced, and theirtheoretical and actual CO₂ uptake values in mg/g, are shown in Tables4a-c below.

TABLE 4a

Polyethylene Polyethylene Polyethylene Polyethylene glycol glycoldimethyl glycol dimethyl glycol dimethyl dibutyl ether ether (Genosorbether (Genosorb ether (Genosorb (Genosorb 1843) - 1753) - CO₂ uptake300) - CO₂ uptake 1900) - CO₂ uptake CO₂ uptake mg/g mg/g (mmol/g) mg/g(mmol/g) mg/g (mmol/g) (mmol/g) Wt % Exp. Cal. Exp. Cal. Exp. Exp. Cal.Cal.  9.23  5.64 6.7 7.3  (0.21)  (0.13)  (0.15)  (0.17) Zeolite 12.522.58 22.64 16.18 18.61 15.93  19.6   19.24 20.14 Rho  (0.51)  (0.51) (0.37)  (0.42)  (0.36)  (0.45)  (0.44)  (0.46) 25   33.2  33.6  — — — —— —  (0.75)  (0.76) PAF-1 12.5 31.91 31.23 — — — — — —  (0.76)  (0.71)ZIF-8 12.5  5.64 13.04 — — — — — —  (0.13)  (0.30) Al(fum) 12.5 11.7820.12 — — — — — — (OH)  (0.27)  (0.46)

Polypropylene glycol - CO₂ uptake mg/g (mmol/g) Wt % Exp. Cal. ZeoliteRho 12.5  15.69   18.96   (0.36)  (0.43) 25   — — PAF-1 — — ZIF-8 — —Al(fum)(OH) — —

TABLE 4b

polyethylene glycol dibenzoate - CO₂ uptake Polyethylene glycolbis(2-ethylhexanoate) - CO₂ mg/g (mmol/g) uptake mg/g (mmol/g) Wt % Exp.Cal. Exp. Cal. 2.8 7.91 (0.063) (0.18) Zeolite Rho 12.5 16.65 17.0114.23 21.48 (0.39) (0.39) (0.33) (0.49) 25   — — — — ZIF-8 12.5 6.7 7.0511.30 11.52 (0.15) (0.16) (0.26) (0.26) 25   — — 14.84 15.13 Al(fum)(OH)12.5 — — — — Zeolite 10A 12.5 — — — —      

     

poly(ethylene glycol) dimethacrylate - CO₂ 15-crown-5 - CO₂ uptakeSilicone oil (50cst) - CO₂ uptake mg/g (mmol/g) mg/g (mmol/g) uptakemg/g (mmol/g) Wt % Exp. Exp. Exp. Cal. Exp. Cal. 4.53 4.37 9.38 (0.10)(0.099) (0.21) Zeolite Rho 12.5 — — 18.71 17.57 20.23 18.92 (0.43)(0.40) (0.46) (0.43) 25   — — — — — — ZIF-8 12.5 7.41 8.91 4.40 9.689.68 9.24 (0.17) (0.20) (0.10) (0.22) (0.22) (0.21) 25   — — — — — —Al(fum)(OH) 12.5 — — — — 15.84 16.28 (0.36) (0.37) Zeolite 10A 12.5 — —— — 20.25 20.68 (0.46) (0.47)

TABLE 4c    

Trioctylamine - CO₂ 2-(tert-butylamino)ethyl uptake mg/g methacrylate -CO₂ uptake (mmol/g) mg/g (mmol/g) Wt % Exp. Cal. Exp. Cal. 2.92 6.33(0.066) (0.14) Zeolite 12.5 18.85 17.12 15.44 20.10 Rho (0.43) (0.39)(0.35) (0.46)      

Tributyl phosphate - CO₂ uptake mg/g Dioctyl phthalate - CO₂ uptake mg/g(mmol/g) (mmol/g) Wt % Exp. Exp. Exp. Cal. 2.65 3.54 (0.06) (0.09)Zeolite 12.5 17.65 16.88 18.71 17.66 Rho (0.40) (0.38) (0.43) (0.40)

Bis(2-ethylhexyl) sebacate - CO₂ uptake mg/g (mmol/g) Exp. Cal.   9.38  (0.21) Zeolite 12.5  23.65   22.77  Rho  (0.54)  (0.52)

CH₄ Uptake

CH₄ uptake of the dispersions was also investigated and the results areshown in Table 5 below. This was carried out using the isochoric methoddescribed above (ie S. L. James et. al.; Nature, 527, 216).

TABLE 5 Table 4c

Tributyl phosphate - Polypropylene glycol - CH₄ uptake mg/g CH₄ uptakemg/g (mmol/g) (mmol/g) Wt % Exp. Cal. Exp. Exp. — 0.457 (0.028) Zeolite12.5 0.181 — 0.466 0.502 Rho (0.011) (0.029) (0.031) 25   — — 0.5060.547 (0.031) (0.034)

Selectivity

Selectivity is estimated by ratio (A_(mmol/g)/B_(mmol/g)). Values forCO₂ selectivity over CH₄ (CO₂/CH₄) were calculated for two of thedispersions and the results are shown in Table 6 below.

TABLE 6

 

Tributyl phosphate - Polypropylene glycol - CO₂/CH₄ selectivity CO₂/CH₄selectivity (by 1:1 ratio) (by 1:1 ratio) Wt % Exp. Cal. Exp. Exp. —c.a. 7.5  Zeolite 12.5 c.a. 36.4 — c.a. 17.6 c.a. 16.5 Rho 25   — — c.a.24.1 c.a. 22.4

The invention claimed is:
 1. A dispersion comprising porous particlesdispersed in a liquid, wherein the porous particles comprise a zeolitewith a mean pore diameter of 1.9 Ångstroms to 4.0 Ångstroms and theliquid does not enter the pores of the zeolite.
 2. The dispersion asclaimed in claim 1, wherein the zeolite is selected from the groupconsisting of zeolite Rho, zeolite Na-Rho, ECR-18, ZSM-25 and PST-20. 3.The dispersion as claimed in claim 1, wherein the zeolite is zeoliteRho.
 4. The dispersion as claimed in claim 1, wherein the liquid isselected from a glycol, 15-crown-5, trioctylamine,2-(tert-butylamino)ethyl methacrylate, tributyl phosphate, dioctylphthalate and bis(2-ethylhexyl) sebacate.
 5. The dispersion as claimedin claim 4, wherein the glycol is a polyalkylene glycol.
 6. Thedispersion as claimed in claim 5, wherein the polyalkylene glycol is apolyethylene glycol or a polypropylene glycol.
 7. The dispersion asclaimed in claim 6, wherein the polyethylene glycol is selected from apolyethylene glycol dialkyl ether and a polyethylene glycol carboxylate.8. The dispersion as claimed in claim 7, wherein the polyethylene glycoldialkyl ether is selected from a polyethylene glycol dimethyl ether anda polyethylene glycol dibutyl ether.
 9. The dispersion as claimed inclaim 1 comprising 0.1-50 wt % of the porous particles.
 10. Thedispersion as claimed in claim 9 comprising 10-30 wt % of the porousparticles.
 11. A method of adsorbing a gas into a liquid, comprising atleast the step of bringing the gas into contact with a dispersion asclaimed in claim
 1. 12. The method of adsorbing a gas into a liquid asclaimed in claim 11, wherein the gas is selected from CO₂ and CH₄.
 13. Amethod of preparing a dispersion as claimed in claim 1, comprising atleast the step of: mixing (i) porous particles comprising the zeolite,and (ii) the liquid.
 14. An assemblage of a dispersion as claimed inclaim 1, the zeolite comprising a cavity and a gas contained within thecavity.
 15. The assemblage as claimed in claim 14, wherein the gas isselected from CO₂ and CH₄.
 16. A dispersion comprising porous particlesdispersed in a liquid phase, wherein the porous particles comprise azeolite and the liquid phase is a size-excluded liquid, wherein thezeolite is selected from the group consisting of zeolite Rho, zeoliteNa-Rho, ECR-18, ZSM-25 and PST-20.
 17. The dispersion as claimed inclaim 16, wherein the zeolite is zeolite Rho.
 18. The dispersion asclaimed in claim 16, wherein the size-excluded liquid is selected fromthe group consisting of a glycol, 15-crown-5, trioctylamine,2-(tert-butylamino)ethyl methacrylate, tributyl phosphate, dioctylphthalate and bis(2-ethylhexyl) sebacate.
 19. The dispersion as claimedin claim 16 comprising 0.1-50 wt % of the porous particles.
 20. Thedispersion as claimed in claim 19 comprising 10-30 wt % of the porousparticles.